1. Field of the Invention
This invention relates to a process and apparatus for making a composite sheet material wherein a strand is attached transversely to a moving sheet. More particularly, the invention concerns a high speed process and apparatus in which a strand, carried by a reciprocating strand traverse guide that is driven by a rotating cylindrical cam, is looped around pins projecting from a pair of pin conveyors which then transfer the strand from the pins to the surface of the moving sheet.
2. Description of Background Art
Known processes for producing a continuous, cross-direction laydown of strands onto a moving sheet are complex, slow and often unsuitable for use with elastic strands. Typical processes for production of cross-direction elastic features (e.g., a waistband) in a disposable diaper, for example, use the much easier machine-direction strand laydown, followed by a complex, slow, cut-and-turn procedure to orient the strands in the cross-direction. Techniques that produce direct strand laydown in the cross-direction are slow. An example of this is the rotating arm technique, similar to a braiding process. Laydown rates are too slow to be attractive. Increasing the strand pitch will increase rates but also introduces an undesirable machine-direction elasticity. Oscillating or swinging arm procedures have the same limitations. Attempts to increase rate by using simultaneous laydown of multiple strands must incorporate steeper laydown angles and/or machine-direction displacement at intervals. These alterations reduce the effectiveness of the elastic strand and introduce substantial machine-direction elasticity and attendant strand waste.
Processes and apparatus are known in which a continuous filament or strand is laid across and attached to the surface of moving sheet. For example, Estee et al, U.S. Pat. No. 2,812,797, discloses an apparatus for making a laminated fabric. In the apparatus, a sheet is continuously advanced between two endless belts that travel in unison and in the same direction as the sheet. One belt is located at each edge of the sheet and each belt has a series of pins projecting from its surface. A swinging frame traverses a plurality of continuous filaments back and forth across the sheet. At each reversal of the traverse, each filament from the frame is looped around a corresponding pin of the belt. Adhesive is applied to the sheet and the filaments. Then, the filaments are disengaged from the pins and adhered to the sheet surface to form an assembly of filaments and sheet. A cover sheet is placed atop the assembly and passed with the filament/sheet assembly between calender rolls to produce the laminated fabric. In another method, disclosed by Hirsch, U.S. Pat. No. 2,962,080, an endless chain mechanism equipped with spaced apart pins, or a swinging lever mechanism equipped with a thread guide, traverses a thread across a sheet that is moving perpendicularly to the path of the traverse. Outside each edge of the sheet is a moving endless chain, equipped with a plurality of spaced apart pins. The thread from the traversing mechanism, at one end of each traverse path, deposits the thread around a pin on the chain at one edge of the sheet and then at the other end of the traverse path deposits thread on a pin of the chain on the other edge of the sheet. Although this method is suitable for use with non-elastic thread, the method is slow and unsuited for use with elastic thread.
Other methods for traversing filaments or strands across a moving surface to form reinforced sheets, scrims or nets also are known. For example, a reciprocating conveyor is disclosed by Friedrich, U.S. Pat. No. 4,080,232, flaying reads on the outer surface of a rotating cylinder that has barbs projection both edges of the cylindrical surface to restrain the threads and form an open mesh net-like structure. Kelly et al, U.S. Pat. No. 4,600,468, also discloses a method for laying out biased arrays of parallel yams on conveyors equipped with needles to restrain the yarns and adhesively bonding the arrays together to form a bias-laid nonwoven fabric. A rotating arm is disclosed by Persson et al, U.S. Pat. No. 5,221,390, for positioning conventional or elastic threads on xe2x80x9cdogged elementsxe2x80x9d (e.g., pins or studs) projecting from a pair of belts located at the edges of a conveyor path. Merkatoris et al, U.S. Pat. No. 5,000,806, discloses a method and apparatus for applying elastic strand to a disposable diaper by means of canted, spindle-equipped wheels for engaging the elastic strand, moving the strand into a sinuous configuration, stretching the strand and thereafter applying the strand transversely to an advancing component of the diaper.
Each of the above-described methods and apparatuses are complex and do not attain high speeds which are desired for efficient and economical attachment of strand in a transverse direction to a moving substrate. Further, some of these methods are not suited for handling elastic strands.
Though not concerned with the problems associated with attaching strand to moving sheets, various mechanisms for traversing strand across a path are known. For example, Altice et al, U.S. Pat. No. 3,086,722, and Akers et al, U.S. Pat. No. 3,675,863, disclose yarn traversing guides driven by rotating cylindrical cams for high speed winding of yarn packages, such as bobbins, cakes and the like.
The process of the present invention for making a composite sheet material, in which a sheet substrate is advanced in a machine direction and a continuous strand is attached to the surface of the sheet transversely to the machine direction (i.e., in a generally cross-machine direction) comprises the following steps:
advancing in a longitudinal direction a sheet substrate, a first conveyor and second conveyor, the sheet having two lateral edges and an upper and a lower surface and each conveyor having a plurality of spaced apart pins extending therefrom in a direction generally perpendicular to the movement of the conveyor;
supplying a strand with a controlled degree of elongation to an oscillating barrel cam and thread guide device that reciprocates the strand to and from across a traverse path, the traverse path being generally transverse to the longitudinal direction of the advancing sheet substrate, wherein the pattern of the thread guide is controlled by the barrel cam design so as to allow sufficient stroke width and/or reversal dwell time to cause the strand to wrap around the pin on the advancing conveyor without striking the pin or the conveyor;
advancing the conveyors to move the pins through a semicircular path that intersects the traverse path of the strand, thereby causing the strand to loop alternately around a pin on the first conveyor and then on a pin of the second conveyor at each end of the traverse path to form a cross-directional continuous strand array carried by the pins;
applying an adhesive to the strand array and/or the advancing sheet substrate;
transferring the strand array from the pins to the upper surface of the advancing sheet substrate while restraining each edge of the strand array in position on the advancing sheet substrate until the applied adhesive is set to form a strand-sheet assembly;
optionally attaching a cover sheet atop the strand-sheet assembly; and
forwarding the resultant composite sheet material to a windup or further processing.
By generally xe2x80x9ccross-machine directionxe2x80x9d is meant that cross strands can be laid down on the moving sheet substrate at angles of 45-90xc2x0 to the machine direction.
The invention also provides an apparatus for performing the above-described process and a garment having an elastic component made with an elastic composite sheet material of the process.